Circuit interrupter with improved surge suppression

ABSTRACT

A suppression and protection circuit is used in conjunction with a circuit interrupter. In one configuration, a voltage clamping device such as a metal oxide varistor is utilized in a ground fault circuit interrupter product for handling transient surges and overvoltage conditions and is placed in series with a solenoid coil. The suppression and protection circuit includes a crowbar device across the line such as a header spark gap to prevent overvoltages, and a low pass filter such as an LC filter for suppressing transient surges.

This application is a continuation of application Ser. No. 09/829,339,filed Apr. 9, 2001 now U.S. Pat. No. 6,900,972.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to commonly owned application Ser. No.09/812,288, filed Mar. 20, 2001, entitled Circuit Interrupting Devicewith Reset Lockout and Reverse Wiring Protection and Method ofManufacture, by inventors Steven Campolo, Nicholas DiSalvo and WilliamR. Ziegler, which is a continuation-in-part of application Ser. No.09/379,138 filed Aug. 20, 1999, now U.S. Pat. No. 6,246,558, which is acontinuation-in-part of application Ser. No. 09/369,759 filed Aug. 6,1999, now U.S. Pat. No. 6,282,070, which is a continuation-in-part ofapplication Ser. No. 09/138,955, filed Aug. 24, 1998, now U.S. Pat. No.6,040,967, all of which are incorporated herein in their entirety byreference.

This application is related to commonly owned application Ser. No.09/812,875, filed Mar. 20, 2001, entitled Reset Lockout for SlidingLatch GFCI, by inventors Frantz Germain, Stephen Stewart, DavidHerzfeld, Steven Campolo, Nicholas DiSalvo and William R. Ziegler, whichis a continuation-in-part of application Ser. No. 09/688,481 filed Oct.16, 2000, all of which are incorporated herein in their entirety byreference.

This application is related to commonly owned application Ser. No.09/813,683, filed Mar. 21, 2001, now U.S. Pat. No. 6,693,779, entitledIDCI With Reset Lockout and Independent Trip, by inventor Nicholas L.DiSalvo, herein incorporated in its entirety by reference.

This application is related to commonly owned application Ser. No.09/812,601, filed Mar. 20, 2001, now abandoned, entitled Neutral SwitchTest Mechanism for a Circuit Interrupter, by inventors David Y. Chan,James Richter and Gerald N. King, herein incorporated in its entirety byreference.

FIELD OF THE INVENTION

The present invention relates to surge suppression, and in particular tocircuit interrupters and ground fault circuit interrupters (GFCI) andrelated products with enhanced transient suppression and protectioncharacteristics.

BACKGROUND OF THE INVENTION

Known GFCI products typically include a metal oxide varistor (MOV)positioned across the power lines of the GFCI product, with the MOVproviding some surge protection to the GFCI product circuitry byclamping transient voltages to acceptable levels.

An MOV is typically a non-linear resistance that is a very highresistance at below the threshold voltage and is typically modeled as anopen circuit. At voltages above the threshold voltage, the resistance isnearly zero and transient power is dissipated. The amount of energy thatan MOV dissipates is generally related to the size of the device,typically a disc or 14, 20, or 40 mm or the like. A larger MOV typicallydissipates more energy, but take up more space, may be more costly andmay require more open space around the device.

The nature of the clamping and the amount of energy that may bedissipated is determined by the size of the disc and voltage ratingassociated with a disc type MOV. Heretofore, GFCI products havetypically been limited to handling transient voltages of 6 kV at 100 A.A need exists for GFCI products capable of sustaining greater transientconditions.

In addition, due to deregulation of local power authorities, overvoltageconditions may be more prevalent, requiring circuits to survive, forexample, 240 V overvoltage conditions for a 120 V rated product. Whensuch conditions occur, GFCI components such as the MOV in the typicalGFCI may not survive. For example, a MOV in the typical GFCI operatingbeyond its rating at overvoltage may disintegrate, and thus suchconditions may also destroy the rest of the electronics in the GFCIproduct. Furthermore, an MOV may fail by rupturing, exploding origniting. Such failure conditions are potentially dangerous.

A need exists for a surge protection circuit which allows componentssuch as a MOV to survive power conditions exceed voltage and currentratings, and thus enabling a GFCI product to survive overvoltageconditions.

SUMMARY OF THE INVENTION

A suppression and protection circuit is used in conjunction with acircuit interrupter. In an embodiment, a metal oxide varistor (MOV) isutilized in a ground fault circuit interrupter (GFCI) product forhandling transient surges and overvoltage conditions. In an embodiment,the suppression and protection circuit includes a crowbar device acrossthe line such as a header spark gap to prevent overvoltages, and a lowpass filter such as an LC filter for suppressing transient surges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a disclosed suppression andprotection circuit connected between power inputs and the GFCI circuitaccording to an embodiment of the present invention;

FIG. 2 illustrates the circuits and components in FIG. 1 in an exampleembodiment with greater detail;

FIG. 3 illustrates a schematic diagram of a GFCI circuit having asuppression and protection circuit and a grounded neutral reset lockouttest according to an embodiment of the present invention;

FIG. 4 illustrates a schematic diagram of an alternative embodiment ofthe GFCI circuit of FIG. 3, utilizing a gas tube crowbar device:

FIG. 5 a illustrates a spark gap device having a spark gap with a 0.10inch width;

FIG. 5 b illustrates a spark gap device having a spark gap with a 0.40inch width;

FIG. 5 c illustrates a spark gap device having a spark gap with a 0.05inch width;

FIG. 5 d illustrates a spark gap device with a vertical header pin andan angularly oriented header pin;

FIG. 5 e illustrates a spark gap device with two angularly orientedheader pins;

FIG. 6 a illustrates a gas tube device having a spark gap formed by twovertical header pins;

FIG. 6 b illustrates a gas tube device having a spark gap formed by avertical header pin and an angularly oriented header pin;

FIG. 7 a illustrates a hybrid protection circuit for an MOV, having alow pass filter using a Zener diode and a resistor; and FIG. 7 billustrates a hybrid protection circuit for an MOV, having a low passfilter using a Zener diode and an inductor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A circuit interrupted having improved transient and overvoltagesuppression is described. The commonly owned U.S. patent applicationsreferred to above describe circuit interrupting devices and areincorporated herein in their entirety by reference. For example, U.S.application Ser. No. 09/812,288 describes a circuit interrupting devicehaving a reset mechanism with a reset lockout portion. The reset lockoutportion prevents the reestablishing of electrical continuity in openconductive paths if the circuit interrupting portion is non-operational,if an open neutral condition exists or if the device is reverse wired.Furthermore, a GFCI is described in commonly owned U.S. Pat. No.4,595,894 which is incorporated herein by reference in its entirety.

Referring to FIG. 1, the suppression and protection circuit 10 is shownto interface between power inputs 12 and a ground fault circuitinterrupter (GFCI) circuit 14 and/or related products connected to aload 16, with the suppression and protection circuit 10 providingenhanced suppression of transient surges as well as protection fromovervoltage conditions. The circuit 10 includes a filter circuit 18 anda overvoltage prevention component 20, which are described in greaterdetail with reference to FIG. 2.

FIG. 2 illustrates one example embodiment of the circuit 10 and the GFCI14. The GFCI 14 includes a metal oxide varistor (MOV) 22 positionedbetween input power lines as the power inputs 12, for example, analternating current (AC) line connection having a phase line 24 and aneutral line 26. The lines 24, 26 are connected through the overvoltageprevention circuit 20, which in an example embodiment is a spark gapdevice known in the art, and through a ground neutral transformer 28 anda differential or sensing transformer 30 to the load 16, which mayinclude a phase load connection 32 and the neutral load connection 34,as in FIG. 2. A test line 36 may also be provided in a manner known inthe art including, for example, a test switch 38 and a resistor R4having a 15 KΩ resistance. Optionally, a relay 40 and/or circuit breakerknown in the art may be provided, as further described herein,connecting the differential transformer 30 to the load lines 32–34.

A processor 42 of the GFCI 14 is connected via a plurality of pins orconnectors to the transformers 28, 30 in a manner known in the art, forexample, using capacitors C3 and C6–C9, a resistor R4, and a diode D2.In the example embodiment shown in FIG. 2, the resistor R3 has a 100 Ωresistance, and the capacitors C3 and C6–C9 have capacitances of 0.01μF, 100 pF, 0.0033 μF, 10 μF, and 100 pF, respectively, each having avoltage rating of 50 V, except for the capacitor C8 having a voltagerating of 6.3 V.

The processor 42 may be, for example, a model LM1851 ground faultinterrupter controller commercially available from “NATIONALSEMICONDUCTOR”, capable of providing ground fault protection for ACpower outlets in consumer and industrial environments. The processor 42is also connected via its pins/connectors to the MOV 22 in a mannerknown in the art, for example, using capacitors C2 and C4–C5 havingcapacitances of 0.01 μF, 1 μF, and 0.018 μF, respectively, at 50 V; acapacitor C10 having a 680 pF capacitance at 500 V; resistors R1 and R2having 15 kΩ and 2 MΩ resistances, respectively; a diode D1; a rectifierQ1 such as a silicon controlled rectifier (SCR); and a set of diodesD3–D6 forming a bridge circuit or configuration, as shown in FIG. 2.

The MOV 22 as well as the filter circuit 18 are connected to the set ofdiodes D3–D6. In an example embodiment, the filter circuit 18 includesan inductor 44 and a capacitor 46, labeled C1 in FIG. 2 and having acapacitance of, for example, 0.01 μF at 400 V. In this example, thefilter circuit 18 functions as an LC low pass filter for input powerapplied to the MOV 22.

The inductor 44 may be a solenoid bobbin acting as a trip coil, suchthat the inductor 44 also functions as an actuator to disengage therelay mechanism 40 on the load side. The capacitor C1 46 may be normallypresent in the GFCI product 14 as a by-pass capacitor. In the disclosedcircuit 10, the capacitor C1 46 serves as a by-pass capacitor as well asthe capacitance in the LC filter of the filter circuit 18.

In the embodiment shown in FIG. 2, the MOV 22 clamps the voltage exposedto the capacitor C1 46 to be within the voltage rating of the capacitor46, for example, 400 V. In one example, transient voltage surges of 3 kVor higher are thus clamped down to 400 V or less. As in the prior art,the MOV 22 itself in a GFCI product 14 is capable of handling transientsurges and overvoltage conditions of, for example, less than 3 kV at 3kA such as a 100 A surge. Using the LC low pass filter 18 in thedisclosed suppression and protection circuit 10, transient voltagesexceeding, for example, 3 kV at 3 kA and even 6 kV at 3 kA, aresuppressed. Accordingly, the MOV 22 in the GFCI product 14 is capable ofhanding voltages exceeding a root-mean-square (RMS) voltage rating ofthe MOV 22, permitting the MOV 22 to survive and provide protection fromother transient, surge, and overvoltage conditions, as described herein.Test transients are often configured with standard pulse ramp up andduration time waveforms.

Continuing with FIG. 2, in another embodiment for providing overvoltageprotection, the overvoltage prevention circuit 20 includes the spark gap48 which generates arcs across its terminals to perform a breakover attransients exceeding a predetermined voltage, such as 3 kV, and furtherprovides multi-mode surge protection and transient suppression. Whenbreakover occurs, the resulting voltage to the transformer 28 isapproximately 200 V. In addition, the filter 18 also functions to limitthe current to which the MOV 22 is exposed during an overvoltage surgecondition. Accordingly, when the current in the MOV 22 is thus limited,the exposure of the MOV 22 to RMS voltages beyond the RMS voltage ratingof the MOV 22 does not damage the MOV 22, and further, does not damagethe rest of the GFCI circuit 14.

In this manner, existing components are combined with other knowncomponents to be used as a low pass filter 18 and to cooperate andfunction with a spark gap device 48 to significantly improve surgesuppression and overvoltage protection.

Referring to FIGS. 3 and 4, embodiments of the present invention aredescribed. In FIG. 3, as in the above embodiment, an LC low pass filteris utilized 44′. The MOV 22′ is a variable resistance that may have aneffect as voltage changes. Similarly a crowbar device 48′ is utilized.

In FIG. 4, as in the above embodiment, an LC low pass filter is utilized44″. The MOV 22″ is a variable resistance that may have an effect asvoltage changes. Similarly a gas tube crowbar device 48″ is utilized.

As can be appreciated, a high frequency transient can be attenuated by aseries low pass filter. Additionally, a transient may be diverted byabsorbing it in a device capable of absorbing energy or shunting it awayfrom a sensate load.

Voltage clamping devices include without limitation selenium cells,Zener diodes, silicon carbide varistors and metal oxide varistors MOVs.An MOV has a generally fast response time and are commonly used fortransient suppression. An MOV will hold a line voltage down while adisproportionately high current flows through it. Source impedance maybe relied upon for clamping.

There is uncertainty as to the long term effects on an MOV that isexposed to repeated transient surges and whether there are “aging”effects. While an MOV may or may not continuously degrade as it isexposed to transient voltages, reducing the energy level to the MOV willincrease the likelihood that a transient may be suppressed anddownstream devices protected.

MOV devices may theoretically be utilized in parallel to absorb moreenergy. However such devices may have to be closely matched so that theywould each be turned on by a transient at nearly the same time. Ofcourse, if one MOV turned on first, it would absorb the full transient.Further, the use of two devices would require greater space and spacing.Such a configuration would also be more costly.

Accordingly a GFCI according to an embodiment of the present inventionwill reduce energy delivered to the MOV.

Crowbar devices may be utilized as a transient suppressor to diverttransients and protect against overvoltage conditions. Such a devicewill typically short a transient to the return. Crowbar device caninclude, without limitation, spark gaps, gas tubes and carbon-blockprotectors. Generally the gas (air for a header spark gap) mustavalanche before the crowbar effect is initiated. Accordingly, a 0.10″space header may have too large a gap to provide avalanche in air at anacceptable voltage level for use as a surge suppressor on an AC powerline. Accordingly, a more narrow spark gap may be selected.

For example, an over 3000 volt transient may break down across a sparkgap and the rest of the circuit will be exposed to an approximately 200Vresulting voltage that an MOV may safely suppress. Similarly in anovervoltage condition of 240V, a low pass filter will limit the currentthat the MOV is exposed to allowing the MOV to survive beyond itsrating.

Referring to FIGS. 5 a–5 c, various spark gap configurations are shownhaving differing spark gap widths. As can be appreciated, varyingsuppression effects may be had with the differing gaps of devices 110,111 and 112. At header pins 114 and 116 at sufficiently high voltages,the air or gas in between the header pins will become ionized and aplasma will develop that will dissipate energy and crowbar the transientvoltage to a lower value. As can be appreciated, the base 118 shouldwithstand the spark energy. The arc or forward drop during the dischargeis low such that the device can carry current to a return path without arelatively large power dissipation in the device.

Referring to FIGS. 5 d–5 e, configurations of a spark gap utilizing adevice and related phenomena referred to as a Jacob's ladder aredescribed 140, 141. As can be appreciated, having one or two of theheader pins 144, 146, 147 at an angle produce a varying spark gapincreasing in the vertical direction that will have a varyingsuppression effect as the spark “walks” up the gap. As can beappreciated, the base 148 should withstand the spark energy.

As can be appreciated, humidity may effect the performance of a sparkgap. Accordingly, measures to avoid humid air such as encapsulating thespark gap may be utilized.

Referring to FIGS. 6 a–6 b, various gas tube configurations are shownhaving differing spark gap widths and may be used as device 48″. As canbe appreciated, varying suppression effects may be had with thediffering gaps of devices 150 and 151. At header pins 154 and 156 atsufficiently high voltages, the air or gas in between the header pinswill become ionized and a plasma will develop that will dissipate energyand crowbar the transient voltage to a lower value. As can beappreciated, the base 158 should withstand the spark energy.

As can be appreciated, the gas 152 may be contained by tube 153.Connectors 155 and 157 provide connections. Other suitable materials 152may be utilized in the spark gap.

Referring to FIGS. 7 a and 7 b, a hybrid protection circuit may protectthe MOV. The voltage clamp device MOV 180 may be in parallel with a lowpass filter or another voltage clamping device such as a Zener diode 182and a resistor 184 or inductor 186.

Additionally, it is known in the art to provide a visual indication thata device equipped with surge suppression is still operating with surgesuppression capability. In an embodiment of the present invention, avisual indicator is provided to indicate that the device is operatingwith adequate surge suppression capability. Similarly, an alarm such asan audio indicator may be provided to indicate that the device is nolonger operating with adequate surge suppression capabilities.

While there have been shown and described and pointed out thefundamental features of the invention, it will be understood thatvarious omissions and substitutions and changes of the form and detailsof the device described and illustrated and in its operation may be madeby those skilled in the art, without departing from the spirit of theinvention.

1. A ground fault circuit interrupter (GFCI) comprising: a housing; atleast one input conductor disposed at least partially within saidhousing and capable of being electrically connected to a source ofelectricity; at least one output conductor disposed within said housingand capable of conducting electrical current to a load when electricallyconnected to said at least one input conductor; a circuit interrupterdisposed within said housing and configured to break said electricalconnection between said input and output conductors in response to theoccurrence of a ground fault or test cycle; a reset mechanism having areset lock-out responsive to the activation of said circuit interrupterso as to be movable between a lock-out position wherein said resetlock-out inhibits resetting of said electrical connection between saidinput and output conductors and a reset position wherein said resetlock-out does not inhibit resetting of said electrical connectionbetween said input and output conductors, wherein when said resetmechanism is activated said circuit interrupter is activated tofacilitate movement of said reset lock-out from said lock-out positionto said reset position by said reset mechanism and resets saidelectrical connection between said input and output conductors; and afirst mode of surge protection for protecting the GFCI during an overvoltage condition comprising a capacitor coupled in series with asolenoid coil of the GFCI to provide a low pass filter connected acrossthe phase and neutral conductors of the GFCI to pass low frequencyvoltage signals to the GFCI circuit while blocking high frequencysignals.
 2. The ground fault circuit interrupter of claim 1 having asecond mode of surge protection comprising: a surge protector coupled inparallel with the capacitor of the low pass filter.
 3. The ground faultcircuit interrupter of claim 2 wherein the surge protector coupled inparallel with the capacitor comprises a metal oxide varistor to shunt amoderate over voltage around the capacitor.
 4. The ground fault circuitinterrupter of claim 3 having a third mode of surge protectioncomprising: an over voltage prevention circuit coupled between the phaseand neutral conductors of the GFCI to shunt a severe over voltagebetween the phase and neutral conductors.
 5. The ground fault circuitinterrupter of claim 4 wherein the over voltage prevention circuitcomprises a spark gap device coupled between the phase and neutralconductors.